Earth leakage clamp tester problem

[Sparkboy]

Hi there,

I have a question regarding the metrel md9270 and a reading I had today.

Basically the client had a trip issue that surfaces every once in a blue moon, I went on Sunday as they had no power from the trip, I found a kettle base with 14.4ma without the kettle on it, Fluctuating from 4ma to 14.4ma and thought straight away that this was faulty, and when I put the kettle on it the milliamps rose to 22ma at the highest, I ramp tested the rcbo and found it was quite sensitive with 23ma.

However I thought I had that Sussed, but I got a call today saying it tripped again?

Went round there today and tested everything on the circuit and then tested IR, etc with everything fine.

Went to test the dishwasher as I could not get to that on Sunday as the plinth is glued lol...

And used my usual test lead with earth out, and got a reading from the metrel md9270 that was jumping from 12ma to 60ma, very fast???

Nothing was tripping, but I do not know why it was acting like that???

Is this normal?

And also I phoned technical the guy said they never have problems with the metrel md9270, he will get someone to call me, and no one bothered sitting at a job waiting for a call... Not very nice lol

Anyway I have some more questions about the meter but thought I would start light lol

Thanks very much in advance

Sparkboy

 

[Marvo]

And used my usual test lead with earth out, and got a reading from the metrel md9270 that was jumping from 12ma to 60ma, very fast???

How are you testing for leakage? It's better if you clamp both the live and neutral at the same time because you're then seeing exactly what the RCD is seeing.

Start by clamping the live and neutral at the RCD to get a global leakage reading. Then clamp the live and neutral of each circuit (2 lives and 2 neutrals if it's a ring final) and figure out which circuits are problematic. Then finally go around the appliances on the suspect circuits with a test cable that allows you to clamp the live and neutral of the appliance.

The test cable is just a short extension lead with a plug on one end, a janus coupling on the other and a section of outer sheath neatly removed in the middle to enable you to clamp the individual wires.

*edit* as for your questions about the Metrel tester I'm afraid I've never owned or used one so I can't advise I'm afraid

 

[HandySparks]

And used my usual test lead with earth out, and got a reading from the metrel md9270 that was jumping from 12ma to 60ma, very fast???

Nothing was tripping, but I do not know why it was acting like that???

If you're clamping the CPC, then you need to be very sure that the casing/chassis of the equipment isn't connected to earth by some other route. Unlikely with a kettle, but possible with a dishwasher.

For investigating RCD tripping faults, you're better off clamping the L&N together and measuring the differential current, which is what the RCD is monitoring.

Edit: I see that Marvo is thinking along similar lines, but is quicker on the draw.

I have a Metrel MD9270 and I've not had a problem with it.

 

[Marvo]

I think regardless of the tester, if you got a twitchy reading at an appliance then the reading on that particular circuit at the CU should have been equally twitchy and the global reading for the entire installation should also have been twitchy. If not then it's probably user error one way or another.

 

[Sparkboy]

Sorry guys I should have said that I did check the rings line and neutral (all four cables), and that was also jumping instantly from 20ma to 70ma... But not tripping anything?

And it was still twitching with the dishwasher out?

I do always test the L&N tails and the L&N circuits.

As it was an RCBO it was very easy to clamp the L&N

However I did not know that I should test the L&N on the appliance I thought you tested the Earth only at appliance level... Thank you

Anyway would you assume my tester is broken ?

cheers

 

[HandySparks]

Anyway would you assume my tester is broken ?

Sounds possible, but it would be nice to compare with another clamp meter on the same circuit.

Also, make sure that the point where the ends of the clamp meet are clear of any debris which might stop the two halves of the core touching properly. And try a new battery.

 

[Marvo]

Not sure if it's broken or it's giving erroneous reading due to something upsetting it. I'd run a series of tests in a controlled environment against another known-good tester to check its functionality. If theresany cause for concern then send it in for testing and calibration.

I had a very expensive power analyzer connected to a network a few months ago. After 3 days of monitoring when we dumped the dataset onto the PC we got nothing but ridiculous readings, one evening it showed the peak load at 4 x the rating of the supply when the place was closed and no equipment was running. After investigation it was a data over power network system they were using between two of the offices that just caused chaos with the instrument.

 

[Sparkboy]

I used it last week and it seemed fine, I found a faulty megaflo stat causing tripping after long tests.

I would never had found that trip without it!

however it is only two weeks old?

but I did notice that if I laid the meter on its side it stays at 0.00 when clamping an item with no leakage, but if laid on its back it would occasionally do tiny jumps of 0.10ma. But I assumed that reading such low values could sometimes have tiny fluctuations ?

thanks again guys for your prompt support, will check out in more detail when I next get the call.

Sparkboy

 

[crow11]

try a new battery like handysparks suggested, i have the di log and mine was doing exactly the same, if i just put it down and switched it on it kept jumping about, put new battery in and all was well, might not be your problem but won't cost much to find out

 

[Sparkboy]

I changed the batteries today, It still seems a little jumpy when checking an appliance with no leakage, when the tester is on it's back it occasionally shows 0.10ma then back to 0.00ma

But I cannot replicate the twitchy readings I was getting from that RCBO on that job, however I have not had a call regarding any more trips?

I have never pat tested anything before but wanted to in the future.

Would a pat test of the appliance pick up an earth leakage fault? I was thinking of buying a seaward prime 100 and pat testing books, and going forward would the seaward prime 100 be a good pat tester for me?

What I am trying to ask is would a pat tester be a good tool in my arsenal for fault finding?

Still no call from metrel a little disappointed with there technical support!


Sparkboy

 

[IzzyS]

I check my clamp meter for accuracy by clamping one of my calibrated MFT leads. Run the ½xDelta n RCD test (as it should last for 2 seconds) @ 10mA, 30mA (and 100mA if you're on a non-RCD circuit) and make sure you get the appropriate reading. If not, get your meter checked out...